1. Brief Statement of the Invention
This invention relates to a combustion detector and, in particular, to combustion apparatus provided with a safety shutoff system in its fuel supply.
2. Brief Statement of the Prior Art
Combustion apparatus such as gas and oil burners and the like have been provided with safety controls that include a shutoff valve in the fuel supply lines with a combustion detection facility such as a thermocouple positioned adjacent the pilot burner of the apparatus whereby the shutoff valve is maintained open only when a flame is present at the pilot burner. Another type of safety control employed in industrial combustion apparatus includes an optical scanner which is responsive to the light emitted by a flame to produce an electrical output that controls the position of the safety shutoff valve.
The employment of thermocouples as the combustion detector as in most household appliances such as furnaces, water heaters and the like, has some disadvantage in that the thermocouple does not have a rapid response to extinguishment of a burner flame and, therefore, must be employed in combustion equipment provided with a continuously burning pilot burner. Optical scanners such as employed in industrial burners are difficult to adjust and use.
It has also been know that certain metal oxides such as zirconia have the ability to generate an electromotive force by transfer of oxygen therethrough and electrode assemblies employing such metal oxides have been used for measurement of oxygen gradients and for fuel cells. Typical of an electrode assembly is that disclosed in U.S. Pat. No. 3,645,875.